Multi-hulled vessels usually have better maneuverability and a shallower draft than single hulled vessels. However, multi-hulled vessels are not commonly used to transport cargo, particularly across open water where rougher conditions can be experienced. Larger known multi-hulled vessels have the problem that in rough conditions, there can be excessive stress placed on the connections between the hulls, as well as on the hulls themselves, leading to fatigue if the connections are inadequate or requiring additional structural weight to avoid fatigue.
In the transport of bulk liquids, such as liquefied petroleum gas (LPG) or liquid chemicals, it is usual to use large single hulled vessels. These vessels offer an efficient means to hold large quantities of fluid and do not suffer from the stresses borne by multi-hulled vessels. However, such vessels are not suited to inshore and coastal transportation due to their large draft.
It is therefore desirable to provide a vessel capable of carrying sufficient cargo for it to be economic to manufacture and operate, while being able to maneuver in the shallower inshore areas. It is also desirable that the vessel should be able to navigate more open waters where rougher conditions may be experienced.
The conventional construction of small gas carrying vessels has proven to be uneconomic. In particular, there are no vessels that are well adapted to distribute liquefied gas and chemicals to coastal areas of South-East Asia and the Pacific Islands with a draft of less than 4 meters.
Further, it Is desirable to have a vessel that is of a simple construction, to reduce the cost of manufacture and to minimise weight, thus allowing a shallower draft than for conventional vessels, while carrying the same amount of cargo at a reduced cost.
It is an object of the present invention to at least alleviate the abovementioned disadvantages by providing a vessel having a shallow draft, and good maneuverability that also has the ability to navigate coastal waters.
A further object of the present invention is to at least alleviate the problem associated with constructing a vessel without the abovementioned disadvantages, while having the capability to be designed for compliance with the existing design regulations for cargo vessels, including vessels that transport liquefied gas.
Many unconventional cargo carrying vessels with multiple hulls have been proposed. For example, UK Patent Application 2058678 (“A” publication) and U.S. Pat. No. 3,447,502 both describe catamaran type ships having hulls which are intended always to be submerged, and a connecting structure that is intended to be at all times above the water surface. Vertical plate-like struts extend upward from the hulls and provide a comparatively small proportion of the ship's displacement. Although claimed to provide reduced wavemaking resistance, having the main parts of the hulls always submerged is unlikely, for a given total displacement, to be as suited to achievement of shallow draft as a vessel in which the hulls are only partially immersed. These patents do not disclose vessels with capacity for relative movement between the hulls. Indeed, the rigid hull connecting structures tend to require a heavier construction, hence greater displacement and draft than vessels having more flexible or articulated connecting structures.
A somewhat different approach is disclosed in patent publication WO91/11359. This discloses a catamaran with very long unsubmerged hulls to achieve the required displacement, with low draft, low wave-making resistance, and a degree of wave piercing capability. However, there is no disclosure of flexible hull connecting structure(s) as a way of reducing overall structural weight and displacement. The rigid connecting structure and the very long hulls would be likely to have the consequence of greater structure weight and hence draft, for a given cargo-carrying capacity than a vessel with flexibly-connected hulls.
Multiple-hull vessels have also been proposed which do allow relative movement of the hulls. An example is WO 97/02982 which discloses a small vessel having two hulls or pontoons and a connecting structure with flexible shaft-like transverse members. These are connected to the pontoons in a manner suited for quick release and extend directly between the pontoons, rather than above them. French patent publication 2546474 A1 discloses a high speed waterborne craft with supporting floats connected to a central module by connecting structures. The connecting structures are evidently intended to deflect, and are pivotally connected to the floats, so that relative motion of the floats is possible. A similar vessel Is disclosed in patent publication DE 2331386 A1, having floats supported by flexible (eg fiberglass) outriggers and fluid-type shock absorbers pivotally secured to the floats to damp their movements.
Another multiple hull vessel allowing some relative motion between hulls is disclosed in patent publication DD 301687 A7. The vessel has two hulls and a connecting structure that appears to be rigid, the relative motion of the hulls being made possible by resilient inserts connecting legs of the connecting structure and the hulls. The inserts are received in wells in the hulls.
Still another vessel with multiple hulls and a connecting structure capable of some deflection to allow for relative movement of the hulls is disclosed in UK patent publication 2152440 A. The connection between connecting structure and hulls is not fully, rigid In that steering is accomplished by rotation of some or all of the hulls about a vertical axis through their connection points. There is no specific disclosure of horizontally elongate hulls. To the contrary, the hulls shown are vertically elongate hydrofoil shaped bodies, that are not well suited to the achievement of shallow draft.
Patent publication EP 0050685 A1 describes a catamaran with flexible connecting frames. To assemble the craft, depending parts of these frames are inserted into sockets in the upper sides of the hulls, which are of round cross-section. The connections between the frames and the hulls is not such as to ensure that frame deflections are lower at the connections than elsewhere in the frames. There is no disclosure of hulls that are adapted for the carrying of cargo.